U.S. patent application number 16/660738 was filed with the patent office on 2020-04-23 for semiconductor device for switching power supply control and ac-dc converter.
This patent application is currently assigned to MITSUMI ELECTRIC CO., LTD.. The applicant listed for this patent is Hiroki ARIMA MATSUDA. Invention is credited to Satoshi ARIMA, Hiroki MATSUDA.
Application Number | 20200127555 16/660738 |
Document ID | / |
Family ID | 70279801 |
Filed Date | 2020-04-23 |
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United States Patent
Application |
20200127555 |
Kind Code |
A1 |
MATSUDA; Hiroki ; et
al. |
April 23, 2020 |
SEMICONDUCTOR DEVICE FOR SWITCHING POWER SUPPLY CONTROL AND AC-DC
CONVERTER
Abstract
Disclosed is a semiconductor device for switching power supply
control including: a high voltage input starting terminal; a
discharger; and an input state detection circuit that includes: a
voltage divider; a peak hold circuit; a first comparator which
detects generation of a plug removal state; a second comparator
which detects generation of a brownout state; a timer circuit; and
a control signal generation circuit which generates a signal to
turn on the discharger or a signal to stop outputting of a
switching control signal, Td1, Td2 and Td3 are set to have a
relationship of Td1<Td2<Td3, Td1 being a delay time until the
capacitor is discharged, Td2 being a delay time for determining the
plug removal state, and Td3 being a delay time for determining the
brownout state, and at least the delay time Td2 and the delay time
Td3 are measured by a common timer circuit.
Inventors: |
MATSUDA; Hiroki; (Zama-shi,
JP) ; ARIMA; Satoshi; (Isehara-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MATSUDA; Hiroki
ARIMA; Satoshi |
Zama-shi
Isehara-shi |
|
JP
JP |
|
|
Assignee: |
MITSUMI ELECTRIC CO., LTD.
Tokyo
JP
|
Family ID: |
70279801 |
Appl. No.: |
16/660738 |
Filed: |
October 22, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 2001/0032 20130101;
H02M 1/36 20130101; H02M 3/33523 20130101; H02M 1/32 20130101; H02M
2001/322 20130101 |
International
Class: |
H02M 1/32 20060101
H02M001/32; H02M 3/335 20060101 H02M003/335; H02M 1/36 20060101
H02M001/36 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2018 |
JP |
2018-199394 |
Claims
1. A semiconductor device for switching power supply control
comprising: a high voltage input starting terminal to which a
voltage obtained by rectifying an alternating current voltage is
input; a discharger which is provided between the high voltage
input starting terminal and a ground point; and an input state
detection circuit which is connected to the high voltage input
starting terminal and detects an input state of the alternating
current voltage, wherein the input state detection circuit
includes: a voltage divider which includes a high withstand voltage
resistor that divides the voltage of the high voltage input
starting terminal; a peak hold circuit which includes a capacitor
and a discharge switch of the capacitor, and holds a peak voltage
of a voltage divided by the voltage divider; a first comparator
which compares the voltage divided by the voltage divider with a
voltage obtained by proportional reduction of the voltage held by
the peak hold circuit, and which detects generation of a plug
removal state; a second comparator which compares the voltage
divided by the voltage divider with a predetermined voltage, and
detects generation of a brownout state; a timer circuit which
measures a predetermined time that is set in advance; and a control
signal generation circuit which generates a signal to turn on the
discharger or a signal to stop outputting of a switching control
signal based on an output of the timer circuit, Td1, Td2 and Td3
are set to have a relationship of Td1<Td2<Td3, Td1 being a
delay time until the capacitor is discharged after an output of the
second comparator is changed in accordance with decrease of an
alternating current input, Td2 being a delay time for determining
the plug removal state, and Td3 being a delay time for determining
the brownout state, and at least the delay time Td2 and the delay
time Td3 are measured by a common timer circuit.
2. The semiconductor device for switching power supply control
according to claim 1, comprising: a clock generation circuit which
generates a clock signal of a predetermined period; and a switching
control signal generation circuit which generates the switching
control signal based on the clock signal from the clock generation
circuit, wherein in response to that the delay time Td2 is measured
by the timer circuit, the control signal generation circuit
generates and outputs a control signal for turning on the
discharger, and in response to that the delay time Td3 is measured
by the timer circuit, the control signal generation circuit
generates a brownout detection signal and supplies the generated
brownout detection signal to the switching control signal
generation circuit to stop outputting of the switching control
signal.
3. The semiconductor device for switching power supply control
according to claim 1, wherein the control signal generation circuit
generates a control signal for turning on the discharge switch of
the peak hold circuit to discharge the capacitor in response to
that the delay time Td1 is measured by the timer circuit.
4. The semiconductor device for switching power supply control
according to claim 1, wherein the common timer circuit is reset and
starts a time measuring operation in response to output change of
the first comparator and the second comparator, and resetting of
the timer circuit is prohibited even when an output of the first
comparator changes, until the second comparator detects start of
the brownout state and the delay time Td3 elapses.
5. The semiconductor device for switching power supply control
according to claim 1, wherein the common timer circuit measures the
delay time Td1, the delay time Td2, and the delay time Td3.
6. The semiconductor device for switching power supply control
according to claim 1, comprising: a switch which is connected
between the high voltage input starting terminal and a power supply
terminal to which a voltage obtained by rectifying an induced
voltage in an auxiliary winding wire of a transformer is applied;
and a starting control circuit which controls the switch when a
voltage is applied to the high voltage input starting terminal,
wherein the switch includes a depression type N-channel MOS
transistor with a high withstand voltage, and the discharger is
connected in series with the switch between the high voltage input
starting terminal and the ground point.
7. An AC-DC converter comprising: the semiconductor device for
switching power supply control according to claim 1; a transformer
which includes an auxiliary winding wire and in which a voltage
obtained by rectifying an alternating current voltage is applied to
a primary-side winding wire; and a switching element which is
connected to the primary-side winding wire, wherein the switching
element is controlled by using the semiconductor device for
switching power supply control.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2018-199394, filed on Oct. 23, 2018, the entire contents of which
are incorporated herein by reference.
BACKGROUND
Technical Field
[0002] The present invention relates to a semiconductor device for
power supply control, and particularly to a technique which is
effectively used in a semiconductor device for primary-side control
that is included in a switching power supply device provided with a
transformer for voltage conversion, and in an AC-DC converter using
the semiconductor device for primary-side control.
Background Art
[0003] Examples of a direct current power supply device include an
isolated AC-DC converter of switching power supply control method
which is configured by including a diode bridge circuit that
rectifies an alternating current power supply, a DC-DC converter
that reduces the direct current voltage rectified in the diode
bridge circuit to convert the voltage into a direct current voltage
of a desired electric potential, and the like.
[0004] In a general isolated AC-DC converter, an X capacitor is
connected between AC terminals in order to attenuate the normal
mode noise, and a resistor for discharging is connected in parallel
with the X capacitor in order to rapidly discharge the electric
charges remaining in the X capacitor when a plug is removed from
the outlet.
[0005] However, in the AC-DC converter in which the resistor for
discharging is connected in parallel with the X capacitor, the
electric power is constantly consumed during connection of the Ac
power supply, which causes increase of the standby power
consumption during the no-load state and during standby.
[0006] Thus, in order to reduce the power consumption during
standby, there are suggested inventions which can promptly
discharge the remaining electric charges in the X capacitor when
the plug removal is detected, by providing a switch for discharging
of the X capacitor in the semiconductor device for power supply
control (for example, see JP 2012-170289 A and JP 2016-158310
A).
[0007] As a semiconductor device for power supply control included
in a switching power supply device, there is a semiconductor device
for power supply control which has a brownout detection function of
detecting a brownout state and stopping the switching control, the
brownout state being a state in which the AC input voltage
decreases to be equal to or lower than a predetermined voltage
continuously for a certain time or more (see JP 5343393 B2). The
semiconductor device for switching power supply control disclosed
in JP 5343393 B2 includes a starting circuit and a comparator which
detects the generation of the brownout state. By detecting the
brownout only in the off state of the starting circuit, a common
terminal is used as the current inflow terminal to the starting
circuit and the voltage detection terminal for detecting the
brownout.
[0008] On the other hand, in the semiconductor device for power
supply control disclosed in JP 2016-158310 A, a high voltage input
starting terminal (current inflow terminal) to which the starting
circuit is connected is used for detecting plug removal.
Accordingly, in a case where the power supply control semiconductor
device is provided with a brownout detection function and a
discharging function of the X capacitor and the high voltage input
starting terminal is used as a detection terminal for both
functions, it is greatly important to accurately detect the
brownout state and the plug removal state and execute the
corresponding operation.
[0009] In addition, the invention of JP 2016-158310 A uses a timer
circuit for detecting a duration of the plug removal state, and the
invention of JP 5343393 B2 uses a delay circuit (timer circuit) for
detecting a duration of the brownout state. If a timer circuit
which measures a time such as several ten milliseconds (ms) is to
be provided, the possession area of the circuit becomes very large.
Thus, in a case of providing both of the brownout detection
function and the X capacitor discharging function to the
semiconductor device for power supply control, if separate timer
circuits are provided for the respective functions, there is a
problem that the chip size increases and the noise easily occurs
when a plurality of timer circuits operate at the same time.
SUMMARY
[0010] The present invention has been made in consideration of the
above problems, and an object of the present invention is to
provide a semiconductor device for switching power supply control
and an AC-DC converter which can accurately detect the brownout
state and the plug removal state by using a high voltage input
starting terminal as a detection terminal for both of the brownout
detection function and the discharging function of X capacitor when
both of the functions are provided.
[0011] Another object of the present invention is to provide a
semiconductor device for switching power supply control and an
AC-DC converter which can avoid the increase of chip size and
suppress the generation of noise when both of the brownout
detection function and the X capacitor discharging function are
provided.
[0012] To achieve at least one of the abovementioned objects,
according to an aspect of the present invention, there is provided
a semiconductor device for switching power supply control
including: a high voltage input starting terminal to which a
voltage obtained by rectifying an alternating current voltage is
input; a discharger which is provided between the high voltage
input starting terminal and a ground point; and an input state
detection circuit which is connected to the high voltage input
starting terminal and detects an input state of the alternating
current voltage, wherein the input state detection circuit
includes: a voltage divider which includes a high withstand voltage
resistor that divides the voltage of the high voltage input
starting terminal; a peak hold circuit which includes a capacitor
and a discharge switch of the capacitor, and holds a peak voltage
of a voltage divided by the voltage divider; a first comparator
which compares the voltage divided by the voltage divider with a
voltage obtained by proportional reduction of the voltage held by
the peak hold circuit, and which detects generation of a plug
removal state; a second comparator which compares the voltage
divided by the voltage divider with a predetermined voltage, and
detects generation of a brownout state; a timer circuit which
measures a predetermined time that is set in advance; and a control
signal generation circuit which generates a signal to turn on the
discharger or a signal to stop outputting of a switching control
signal based on an output of the timer circuit, Td1, Td2 and Td3
are set to have a relationship of Td1<Td2<Td3, Td1 being a
delay time until the capacitor is discharged after an output of the
second comparator is changed in accordance with decrease of an
alternating current input, Td2 being a delay time for determining
the plug removal state, and Td3 being a delay time for determining
the brownout state, and at least the delay time Td2 and the delay
time Td3 are measured by a common timer circuit.
[0013] Preferably, the semiconductor device for switching power
supply control includes: a clock generation circuit which generates
a clock signal of a predetermined period; and a switching control
signal generation circuit which generates the switching control
signal based on the clock signal from the clock generation circuit,
wherein in response to that the delay time Td2 is measured by the
timer circuit, the control signal generation circuit generates and
outputs a control signal for turning on the discharger, and in
response to that the delay time Td3 is measured by the timer
circuit, the control signal generation circuit generates a brownout
detection signal and supplies the generated brownout detection
signal to the switching control signal generation circuit to stop
outputting of the switching control signal.
[0014] Preferably, in the semiconductor device for switching power
supply control, the control signal generation circuit generates a
control signal for turning on the discharge switch of the peak hold
circuit to discharge the capacitor in response to that the delay
time Td1 is measured by the timer circuit.
[0015] Preferably, in the semiconductor device for switching power
supply control, the common timer circuit is reset and starts a time
measuring operation in response to output change of the first
comparator and the second comparator, and resetting of the timer
circuit is prohibited even when an output of the first comparator
changes, until the second comparator detects start of the brownout
state and the delay time Td3 elapses.
[0016] Preferably, in the semiconductor device for switching power
supply control, the common timer circuit measures the delay time
Td1, the delay time Td2, and the delay time Td3.
[0017] Preferably, the semiconductor device for switching power
supply control includes: a switch which is connected between the
high voltage input starting terminal and a power supply terminal to
which a voltage obtained by rectifying an induced voltage in an
auxiliary winding wire of a transformer is applied; and a starting
control circuit which controls the switch when a voltage is applied
to the high voltage input starting terminal, wherein the switch
includes a depression type N-channel MOS transistor with a high
withstand voltage, and the discharger is connected in series with
the switch between the high voltage input starting terminal and the
ground point.
[0018] According to another aspect of the present invention, there
is provided an AC-DC converter including: the above semiconductor
device for switching power supply control; a transformer which
includes an auxiliary winding wire and and in which a voltage
obtained by rectifying an alternating current voltage is applied to
a primary-side winding wire; and a switching element which is
connected to the primary-side winding wire, wherein the switching
element is controlled by using the semiconductor device for
switching power supply control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The accompanying drawings are not intended as a definition
of the limits of the invention but illustrate embodiments of the
invention, and together with the general description given above
and the detailed description of the embodiments given below, serve
to explain the principles of the invention, wherein:
[0020] FIG. 1 is a circuit configuration view showing an embodiment
of an AC-DC converter as an isolated direct current power supply
device according to the present invention;
[0021] FIG. 2 is a circuit configuration view showing a
configuration example of a primary-side switching power supply
control circuit (power supply control IC) of a transformer in the
AC-DC converter in FIG. 1;
[0022] FIG. 3 is a circuit configuration view showing a
configuration example of a starting circuit and a brownout and plug
removal detection circuit included in the power supply control IC
in the example;
[0023] FIG. 4 is a circuit configuration view showing a
configuration example of a timer reset control circuit included in
the brownout and plug removal detection circuit;
[0024] FIG. 5 is a circuit configuration view showing a
configuration example of an identification control circuit included
in the brownout and plug removal detection circuit;
[0025] FIG. 6 is a circuit configuration view showing a
configuration example of a peak hold circuit and a discharge
control circuit included in the brownout and plug removal detection
circuit;
[0026] FIG. 7 is a waveform diagram showing four patterns of output
state of a comparator for detecting plug removal and a comparator
for detecting the brownout generated according to the level of AC
input;
[0027] FIG. 8 is a timing chart showing the operation timing in a
case where the brownout state occurs during the normal switching
control operation, thereafter the AC input shifts to the brown-in
state in which the AC input is sufficiently high, and plug removal
occurs;
[0028] FIG. 9 is a timing chart showing the operation timing in a
case where the AC input shifts to the brownout state during the
normal switching control operation, and plug removal occurs during
the brownout; and
[0029] FIG. 10 is a timing chart showing the operation timing in a
case where the AC input shifts to the brownout state during the
normal switching control operation, and returns in a short time to
the brown-in state in which the AC input is sufficiently high, and
plug removal occurs.
DESCRIPTION OF EMBODIMENTS
[0030] Hereinafter, a preferred embodiment of the present invention
will be described with reference to the drawings.
[0031] FIG. 1 is a circuit configuration view showing an embodiment
of the AC-DC converter as an isolated direct current power supply
device to which a switching power supply control semiconductor
device according to the present invention is applied.
[0032] The AC-DC converter according to this embodiment includes:
an X capacitor Cx connected between AC terminals for attenuating
the normal-mode noise; a noise blocking filter 11 including a
common-mode coil and the like; a diode bridge circuit 12 that
rectifies an alternating current voltage (AC); a smoothing
capacitor C1 that smooths the rectified voltage; a transformer T1
for voltage conversion including a primary-side winding wire Np, a
secondary-side winding wire Ns, and an auxiliary winding wire
Nb.
[0033] The AC-DC converter also includes: a switching transistor SW
including an N-channel MOSFET connected in series with the
primary-side winding wire Np of the transformer T1; and a switching
power supply control semiconductor device 13 that drives the
switching transistor SW. In this embodiment, the switching power
supply control semiconductor device 13 is formed as a semiconductor
integrated circuit (hereinafter referred to as a power supply
control IC) on a single semiconductor chip such as a single-crystal
silicon or the like.
[0034] On the secondary side of the transformer T1, a rectifying
diode D2 connected in series with the secondary-side winding wire
Ns and a smoothing capacitor C2 connected between a cathode
terminal of this diode D2 and the other terminal of the
secondary-side winding wire Ns are provided. By supplying an
electric current intermittently to the primary-side winding wire
Np, the alternating current voltage is induced in the
secondary-side winding wire Ns, and by rectifying and smoothing
this induced alternating current voltage, the direct current
voltage Vout according to the winding wire ratio between the
primary-side winding wire Np and the secondary-side winding wire Ns
is output.
[0035] In addition, on the secondary side of the transformer T1,
there are provided a coil L3 and a capacitor C3 that form a filter
for blocking the switching ripple noise and the like occurring in
the switching operation on the primary side, and there are also
provided a detection circuit 14 for detecting the output voltage
Vout and a photodiode 15a as a light emission-side element of a
photocoupler which is connected to the detection circuit 14 and
transmits a signal corresponding to the detected voltage to the
power supply control IC 13. On the primary side, a phototransistor
15b is provided as a light reception-side element which is
connected between a ground point and a feedback terminal FB of the
power supply control IC 13 and receives a signal from the detection
circuit 14.
[0036] On the primary side of the AC-DC converter according to this
embodiment, there is provided a rectifying/smoothing circuit that
includes a rectifying diode DO connected in series with the
auxiliary winding wire Nb, and a smoothing capacitor C0 connected
between the ground point GND and a cathode terminal of the diode
DO. The voltage rectified and smoothed in the rectifying/smoothing
circuit is applied to a power supply voltage terminal VDD of the
power supply control IC 13.
[0037] The power supply control IC 13 includes a high voltage input
starting terminal HV to which the voltage before being rectified in
the diode bridge circuit 12 is applied through diodes D11 and D12
and a resistor R1. The power supply control IC 13 is configured to
operate by the voltage from this high voltage input starting
terminal HV when the power is input (immediately after a plug is
inserted into an outlet).
[0038] In addition, in the present embodiment, a resistor Rs for
current detection is connected between the ground point GND and a
source terminal of the switching transistor SW, and a resistor R2
is connected between a current detection terminal CS of the power
supply control IC 13 and a connection node N1 between the switching
transistor SW and the current detection resistor Rs. Furthermore, a
capacitor C4 is connected between the ground point and the current
detection terminal CS of the power supply control IC 13. The
resistor R2 and the capacitor C4 form a low-pass filter.
[0039] Next, with reference to FIG. 2, a specific structure example
of the power supply control IC 13 will be described.
[0040] As illustrated in FIG. 2, the power supply control IC 13
according to the example includes: an oscillation circuit 31 that
oscillates at a frequency according to a voltage VFB of a feedback
terminal FB; a clock generation circuit 32 including a circuit like
a one-shot pulse generation circuit that generates a clock signal
CK for providing the timing to turn on the primary-side switching
transistor SW on the basis of an oscillation signal .PHI.c
generated in the oscillation circuit 31; an RS/flip-flop 33 that is
set by the clock signal CK; and a driver (a driving circuit) 34
that generates a driving pulse GATE of the switching transistor SW
in accordance with the output of the flip-flop 33.
[0041] Moreover, the power supply control IC 13 includes: an
amplifier 35 that amplifies the voltage Vcs input to the current
detection terminal CS; a comparator 36a as a voltage comparison
circuit that compares an electric potential Vcs' amplified by the
amplifier 35 with a comparison voltage (threshold voltage) Vocp for
monitoring the overcurrent state; a waveform generation circuit 37
that generates a voltage RAMP with a predetermined waveform on the
basis of the voltage VFB of the feedback terminal FB; a comparator
36b that compares the electric potential Vcs' that is amplified by
the amplifier 35 with the waveform RAMP generated by the waveform
generation circuit 37; and an OR gate G1 that takes the logical sum
of the outputs of the comparators 36a and 36b.
[0042] By the output RS of the OR gate G1 being input to a reset
terminal of the flip-flop 33, the timing to turn off the switching
transistor SW is provided. A pull-up resistor or a constant-current
source is provided between the feedback terminal FB and an internal
power supply voltage terminal, and the electric current flowing in
the phototransistor 15b is converted into a voltage by the
resistor.
[0043] Furthermore, the power supply control IC 13 in the example
includes a frequency control circuit 38 that changes the
oscillation frequency of the oscillation circuit 31, that is, the
switching frequency on the basis of the voltage VFB of the feedback
terminal FB in accordance with a predetermined characteristic.
Although not shown, the oscillation circuit 31 includes a current
source which allows the electric current to flow in accordance with
the voltage from the frequency control circuit 38, and is formed of
an oscillator whose oscillation frequency changes depending on the
amount of the electric current supplied from the current
source.
[0044] The power supply control IC 13 may include a duty limiting
circuit that generates a maximum duty reset signal to limit the
duty (Ton/Tcycle) of the driving pulse GATE so that the duty does
not exceed a prescribed maximum value (for example, 85% to 90%) on
the basis of the clock signal CK output from the clock generation
circuit 32.
[0045] Furthermore, the power supply control IC 13 in the example
includes: a starting switch S0 which is provided between the high
voltage input starting terminal HV and the power supply voltage
terminal VDD; a starting circuit (start circuit) 40 which, when the
voltage is input to the high voltage input starting terminal HV via
the resistor R1, turns on the starting switch S0 to start the IC; a
brownout and plug removal detection circuit 50 which detects the
brownout state and generates a signal to stop the switching
control, and detects whether or not the plug of the AC power supply
is removed from the outlet and generates a signal to turn on the
discharge switch of the X capacitor Cx (FIG. 1); and an internal
power supply circuit 60 which generates the internal power supply
voltage necessary for the operation of the internal circuit on the
basis of the voltage of the power supply voltage terminal VDD.
[0046] FIG. 3 shows a configuration example of the starting circuit
40 and the brownout and plug removal detection circuit 50 and two
regulators included in the internal power supply circuit 60 in the
power supply control IC in FIG. 2.
[0047] As shown in FIG. 3, the internal power supply circuit 60
includes a reference voltage circuit 61 which generates a reference
voltage VREF, a regulator 62 which generates the power supply
voltage of the starting circuit 40 and the brownout and plug
removal detection circuit 50, and a regulator 63 which generates
the power supply voltage of the internal circuit (circuit blocks 31
to 38 shown in FIG. 2). The regulator 62 is configured to continue
the operation when the voltage of the power supply voltage terminal
VDD is equal to or more than a predetermined voltage that is
determined by the characteristic of the regulator. The regulator 63
is configured to be able to stop the operation by a control signal
even if the voltage of the power supply voltage terminal VDD is the
predetermined voltage or more.
[0048] As shown in FIG. 3, there are provided a starting control
circuit 41 controlling the starting switch S0 between the high
voltage input starting terminal HV and the power supply voltage
terminal VDD for controlling starting of the switching power supply
control semiconductor device 13, a voltage division circuit 42
including resistors R3 and R4 that are connected in series between
the power supply voltage terminal VDD and the ground point, and a
comparator 43 to which the divided voltage and the reference
voltage Vref1 are input and which has a hysteresis characteristic.
The starting switch S0 is formed of a depression type N-channel MOS
transistor with a high withstand voltage which is normally turned
on.
[0049] The potential difference between the high voltage input
starting terminal HV and the power supply voltage terminal VDD is
0V before insertion of the plug into the outlet. When a voltage is
applied to the high voltage input starting terminal HV by the
insertion of the plug, an electric current flows from the high
voltage input starting terminal HV to the power supply voltage
terminal VDD through the starting switch S0 that is normally turned
on, the capacitor C0 (FIG. 1) externally provided to the VDD
terminal is charged, and the voltage of the VDD terminal gradually
rises. Accordingly, the high voltage input starting terminal HV
functions as a current inflow terminal.
[0050] The starting control circuit 41 turns off the starting
switch S0 when the VDD terminal reaches a predetermined voltage
such as 21V, for example. When the VDD terminal reaches the
predetermined voltage such as 21V, the regulator 63 operates and
the switching control of the switching transistor SW by the
internal circuit is started. On the other hand, when the VDD
terminal falls to the operation stop voltage (for example,
VDD=6.5V) of the regulator 62, the starting switch S0 is turned on,
and the voltage of the VDD terminal rises again to 21V.
[0051] When the protection function or the brownout detection
function operates, the starting control circuit 41 controls the VDD
terminal voltage within a certain voltage range on the basis of the
output of the comparator 43. The starting control circuit 41 is
configured to repeatedly execute the control of turning on the
starting switch S0 to allow an electric current to flow from the
high voltage input starting terminal HV to the power supply voltage
terminal VDD when the voltage of the VDD terminal falls to 12V, for
example, and of turning off the starting switch S0 to block the
electric current from the high voltage input starting terminal HV
when the voltage of the VDD terminal rises to 13V, for example.
[0052] The starting circuit 40 further includes: an operation start
circuit 44 which constantly monitors the voltage of the power
supply voltage terminal VDD and, when the voltage of VDD reaches a
voltage such as 19.6V, for example, starts the regulator 63 that
generates the power supply voltage of the internal circuit to
generate a signal to start the operation of the internal circuit; a
voltage division circuit 45 formed of resistors R5, R6 connected in
series between the ground point and the power supply voltage
terminal VDD; and an operation stop circuit 46 formed of a
comparator (voltage comparison circuit) which compares the divided
voltage and a reference voltage Vref2, and, when the VDD falls to
6.5V, for example, stops the operation of the internal circuit by
stopping the regulator 63 which generates the internal power supply
voltage. The operation start circuit 44 may be a circuit configured
to be able to detect that the monitoring target becomes a
predetermined voltage or more without using a reference voltage, or
may be configured by a comparator (voltage comparison circuit)
using the reference voltage.
[0053] The output signal of the operation start circuit 44 is input
to a set terminal of an RS flip flop (RS1) 47. The output signal of
the above operation stop circuit 46 is input to a reset terminal of
the RS flip-flop 47 via an OR gate G2, and the output signal of the
flip-flop 47 is supplied as an operation control signal of the
regulator 63 which generates the power supply voltage of the
internal circuit. The above starting control circuit 41 can be
configured by including a resistor which is connected between the
VDD terminal and the gate terminal of the starting switch S0, a
Zener diode which is connected in the opposite direction between
the ground point and the gate terminal of S0, a MOS transistor
which is connected in parallel with the Zener diode, and a logic
circuit which turns on and off the MOS transistor with the signals
from the comparator 43, operation start circuit 44 and operation
stop circuit 46, and the signals BOS and BOE from the brownout and
plug removal detection circuit 50 as inputs, for example.
[0054] In the starting circuit 40, there is provided a discharger
which is formed of a resistor Rd and a switch Sd connected in
series with the starting switch S0 between the high voltage input
starting terminal HV and the ground point. Though the discharger
(Rd, Sd) is shown in the starting circuit 40 in the drawing, the
discharger may be configured as a functional circuit separate from
the starting circuit 40. The switch Sd for discharging can be
configured by an enhancement-type MOS transistor with a middle
withstand voltage, for example.
[0055] The brownout and plug removal detection circuit 50 includes
a voltage division circuit 51 formed of high withstand voltage
resistors R7 and R8 which are connected in series between the high
voltage input starting terminal HV and the ground point, a
comparator 52 which has a hysteresis characteristic for detecting
that the voltage of HV falls to a threshold that is set to be a
voltage which is approximately 2/3 of the peak value of AC input or
less than 100V by comparing the voltage divided by the voltage
division circuit 51 and a reference voltage Vref3, and an RS
flip-flop (RS2) 53 which operates by the output signal of the
inverter INV which inverts the output of the comparator 52. An
inversion output QB of the flip-flop 53 is supplied to the driver
34 (FIG. 2) as an output stop signal GSC to stop the output of the
driving pulse of the switching element SW. Thus, in a case where
the AC power supply is input in a low AC input state, that is, the
power supply control IC is started in the brownout state, an
electric current flows to the VDD terminal by the starting circuit
40 in that state, and the electric potential of VDD terminal
reaches the IC operation start voltage, it is possible not to
output the driving pulse GATE of the switching element SW.
[0056] The brownout and plug removal detection circuit 50 includes:
a timer circuit 54 which measures a predetermined delay time from
the detection of brownout and the detection of plug removal; and an
edge detection circuit 55 which detects the falling edge of the
output signal of the timer circuit 54. The output signal of the
timer circuit 54 is input to the reset terminal of the RS flip-flop
53.
[0057] As the delay time from the detection of brownout and as the
predetermined delay time from the detection of plug removal, 60 ms
and 30 ms can be respectively selected, for example. The timer
circuit 54 is configured to perform the time measuring operation by
the signal of the oscillator formed of a ring oscillator or the
like with the regulator 62 as a power supply.
[0058] Furthermore, the brownout and plug removal detection circuit
50 includes: a peak hold circuit 56A which holds a peak value of
the voltage divided by the voltage division circuit 51 which
divides the voltage of the high voltage input starting terminal HV;
and a comparator 56B which compares the voltage divided by
resistors R9 and R10 connected between the ground point and the
output terminal of the peak hold circuit 56A and the voltage
divided by the voltage division circuit 51. There are also
provided: a timer reset control circuit 57 to which the output of
the comparator 56B and the output signal of the comparator 52 and
the AND gate G3 are input; an identification control circuit 58
which is provided at the subsequent stage of the timer circuit 54;
and a discharge control circuit 59 which generates a discharge
signal of the capacitor (C4 in FIG. 6) included in the peak hold
circuit 56A on the basis of the output of the comparator 56B, the
output of the timer circuit 54, and the output of the
identification control circuit 58.
[0059] In the example, the timer circuit 54 can measure a
predetermined delay time from the detection of brownout and the
detection of plug removal and a delay time of the signal to
discharge the peak hold circuit 56A. The identification control
circuit 58 is configured to determine the plug removal by
measuring, with the timer circuit 54, the time during which the
voltage Vn0 divided by the voltage division circuit 51 is not lower
than the voltage VTH (for example, value of 75% of peak value)
which is obtained by proportional reduction of the voltage held by
the peak hold circuit 56A. In detail, when the state in which the
Vn0 is not lower than the VTH continues for 30 ms, for example, the
identification control circuit 58 determines that the plug removal
occurs, and outputs a discharge signal of the X capacitor. The VTH
which is a threshold level for determining the plug removal is set
to be higher than the brownout detection level at the time of
normal operation with sufficiently high AC input.
[0060] The time measuring operation of the timer circuit 54 is
started by the output signal of the AND gate G3 to which the output
signal of the comparator 52 and the output signal of the flip-flop
47 included in the starting circuit 40 are input. When a
predetermined delay time (for example, 60 ms) elapses from the
detection of brownout, the identification control circuit 58
determines that the AC input is the brownout state on the basis of
the output signal of the timer circuit 54, and outputs the brownout
detection signal BOS. The RS flip-flop 53 is reset by this signal,
and the output stop signal GSC of the driving pulse is output.
[0061] Furthermore, after the stop of outputting by the detection
of brownout, when the voltage of the high voltage input starting
terminal HV rises to invert the output signal of the comparator 52,
the RS flip-flop 53 is set by the inverter INV, the output stop
signal GSC changes to a low level and the output stop state is
released. By the inversion of the output signal of the comparator
52, the output of the AND gate G3 changes to a low level, the
falling is detected by the falling edge detection circuit (DED in
FIG. 4) in the timer reset control circuit 57 and the timer circuit
54 is reset. Thus, the output (TM3) of the timer circuit 54
changes, and the brownout detection signal BOS output from the
identification control circuit 58 which receives the above signal
changes to a low level. The edge detection circuit 55 which detects
the falling edge outputs the brownout end signal (pulse) BOE.
[0062] The brownout end signal (pulse) is configured to reset the
RS flip-flop 47 via the OR gate G2.
[0063] FIG. 4 shows a specific circuit example of the timer rest
control circuit 57 included in the brownout and plug removal
detection circuit 50 in FIG. 3. FIG. 5 shows a specific circuit
example of the identification control circuit 58. FIG. 6 shows a
specific circuit example of a peak hold circuit 56A and a discharge
control circuit 59.
[0064] As shown in FIG. 4, the timer reset control circuit 57
includes: an OR gate G4 to which the output CMP1 of the comparator
56B for detecting plug removal and the output of the AND gate G3
are input; a NAND gate G5 to which the output CMP1 of the
comparator 56B and the output CMP2 of the comparator 52 for
detecting the brownout and the brownout detection signal BOS output
from the identification control circuit 58 are input; an AND gate
G6 to which the output of the NAND gate G5 and the output of the OR
gate G4 are input; a rising edge detection circuit UED which
detects the rising edge of the output of the AND gate G6; and a
falling edge detection circuit DED which detects the falling edge
of the output of the AND gate G6.
[0065] The timer reset control circuit 57 further includes: a NOR
gate G7 to which the output of the rising edge detection circuit
UED and the output of the falling edge detection circuit DED are
input; an AND gate G8 to which an X capacitor discharge signal XCD
output from the identification control circuit 58 and a timeout
signal TM2 of a plug removal detection delay time Td2 output from
the timer circuit 54 are input; and an OR gate G9 to which the
output of the AND gate G8 and the output of the NOR gate G7 are
input; and an AND gate G10 to which a signal obtained by inverting
the brownout end signal BOE output from the identification control
circuit 58 with the inverter INV2 is input. The output of the AND
gate G10 is supplied as the reset signal RST to the timer circuit
54.
[0066] As shown in FIG. 5, the identification control circuit 58
includes: an AND gate G11 to which the output CMP1 of the
comparator 56B for detecting plug removal and the output CMP2 of
the comparator 52 for detecting the brownout are input; a D-type
flip-flop FF1 which takes in a rest signal RST that is the output
of the timer reset control circuit 57 with the output of the AND
gate G11 as a clock signal; an AND gate G12 to which the timeout
signal TM1 of the discharge delay time Td1 of the peak hold circuit
and the timeout signal TM3 of the brownout detection delay time Td3
are input; and an OR gate G13 to which the output of the AND gate
G12 and the signal obtained by inverting the reset signal RST with
the inverter INV3 are input.
[0067] The identification control circuit 58 includes: an OR gate
G14 to which the output of the D-type flip-flop FF1 and an output
signal "DISCHARGE" of the discharge control circuit 59 are input;
an RS flip-flop FF2 which is set and reset by the output of the OR
gate G14 and the output of the OR gate G13; and an AND gate G15 to
which the inverted output of the flip-flop FF2 and the timeout
signal TM2 of the delay time Td2 of the plug removal detection are
input. The output of the AND gate G15 is output as the discharge
signal XCD of the X capacitor.
[0068] The identification control circuit 58 further includes: an
AND gate G20 to which the timeout signal TM3 of the brownout
detection delay time Td3 and the output of the AND gate G3 (FIG. 3)
are input; and an RS flip-flop FF3 which is set and reset by the
output of the AND gate G20 and the signal obtained by inverting the
output of the AND gate G3 with the inverter INV4. The output of the
flip-flop FF3 is output as the brownout detection signal BOS.
[0069] As shown in FIG. 6, the discharge control circuit 59
includes: an RS flip-flop FF4 which is set and reset by a timeout
signal TM1 of the discharge delay time Td1 of the peak hold circuit
and a signal obtained by inverting the output CMP1 of the
comparator 56B for detecting plug removal with the inverter INV 5;
a rising edge detection circuit UED2 which detects a rising edge of
the timeout signal TM1 of the discharge delay time Td1 of the peak
hold circuit; and an AND gate G16 to which the output of the rising
edge detection circuit UED2 and the RS flip-flop FF4 are input.
[0070] The discharge control circuit 59 includes: an AND gate G17
to which the inverted output of the RS flip-flop FF4 and the
brownout detection signal BOS are input; an RS flip-flop FF5 which
is set and reset by the output of the AND gate G17 and the brownout
end signal BOE; and an AND gate G18 to which the inverted output of
the RS flip-flop FF5 and the output of the AND gate G16 are input.
The output of the AND gate G18 is output to the peak hold circuit
56A as an output signal "DISCHARGE" of the discharge control
circuit 59.
[0071] As shown in FIGS. 3 and 6, the peak hold circuit 56A
includes a diode D4 whose anode terminal is connected to a node of
the voltage division circuit 51; a capacitor element C4 which is
connected between the cathode terminal of the diode D4 and the
ground point; a buffer BFF4 formed of a voltage follower whose
input terminal is connected to the connection node between the
diode D4 and the capacitor element C4; and a discharge switch S4
which is connected in parallel with the capacitor element C4. The
electric charges of the capacitor element C4 are discharged by the
discharge switch S4 being turned on by the output signal
"DISCHARGE" of the discharge control circuit 59.
[0072] The discharge signal (pulse) "DISCHARGE" from the discharge
control circuit 59 to the peak hold circuit 56A is set to be output
and turn on the discharge switch S4 when a predetermined time (for
example, 15 ms) elapses from the reset of the timer circuit 54. The
capacitor C4 of the peak hold circuit 56A is discharged in such a
way because it is not possible to accurately detect the plug
removal for discharging of the X capacitor if the previous high
peak value is held when the peak voltage of AC input is lowered.
Thus, the measuring time for discharging of the peak hold circuit
56A by the timer is set to be shorter than the detection time of
discharging of the X capacitor.
[0073] As described above, the brownout detection delay time, the
plug removal detection delay time, and the discharge delay time are
measured by the common timer circuit 54. Thus, it is possible to
reduce the possession area of the circuit and reduce the chip size
of IC compared with a case where timer circuits are separately
provided. The brownout detection delay time, the plug removal
detection delay time, and the discharge delay time are set in a
multiple-relationship such as 60 ms, 30 ms and 15 ms. Thus, in a
case where the timer circuit 54 is formed of a frequency division
circuit having a plurality of flip-flops in a cascade connection,
the time measuring signal of 30 ms may be taken from a half step of
the time measuring signal of 60 ms, and the time measuring signal
of 15 ms may be taken from a quarter step of the time measuring
signal of 60 ms. Thus, there is an advantage that the time
measuring signal (timeout signal) can be generated easily.
[0074] The timer reset control circuit 57 and the identification
control circuit 58 are provided because the states of the output
CMP1 of the comparator 56B (Plugout Comp) for detecting plug
removal and the output CMP2 of the comparator 52 (Brownout Comp)
for detecting the brownout are classified into four cases as shown
in FIGS. 7A to 7D according to the AC input level, and it becomes
difficult to perform setting of the timing to reset the timer when
the above three types of delay times are measured by a common timer
circuit if each of the states is not grasped. In detail, for
example, if the timer circuit 54 is reset in order to start the
time measuring of the discharge delay time during detection of the
brownout, the time measuring of the brownout detection delay time
is interrupted. Thus, such an operation needs to be avoided.
[0075] Among FIGS. 7A to 7D, FIG. 7A is a waveform diagram when the
AC input level is sufficiently high and the power supply control IC
13 performs the normal operation, and the plug removal occurs at a
timing when the AC input is higher than the plug removal detection
level. In this case, both of the outputs CMP1 and CMP2 of the
comparator 56B for detecting plug removal and the comparator 52 for
detecting brownout are at low levels.
[0076] FIG. 7B is a waveform diagram when the AC input level is
sufficiently high and the power supply control IC 13 performs the
normal operation, and the plug removal occurs at a timing when the
AC input is lower than the brownout detection level. In this case,
both of the outputs CMP1 and CMP2 of the comparator 56B for
detecting plug removal and the comparator 52 for detecting brownout
are at high levels.
[0077] FIG. 7C is a waveform diagram when the AC input level is
lower than the brownout detection level, and the plug removal
(Plugout) occurs at a timing when the AC input is higher than the
plug removal detection level. In this case, the output CMP1 of the
comparator 56B for detecting plug removal is at a low level, and
the output CMP2 of the comparator 52 for detecting brownout is at a
high level.
[0078] FIG. 7D is a waveform diagram when the AC input level is
lower than the brownout detection level, and the plug removal
occurs at a timing when the AC input is lower than the brownout
detection level. In this case, both of the outputs CMP1 and CMP2 of
the comparator 56B for detecting plug removal and the comparator 52
for detecting brownout are at high levels.
[0079] As seen from FIGS. 7B and 7D, only in the plug removal
detection and the brownout detection, there occurs a situation
where the respective comparator outputs are the same logic. Thus,
it is not possible to accurately detect the AC input state
(brown-in or brownout) in which the plug was removed. In the
brownout and plug removal detection circuit 50 shown in FIG. 4, it
is possible to accurately detect the brownout state and the plug
removal state by grasping the four states as described above and
resetting the timer circuit 54 according to the respective
states.
[0080] FIG. 8 shows voltage waveforms of the components in the
power supply control IC 13 in a case where the AC input falls
during the switching control operation by the power supply control
IC 13 with a sufficiently high AC input, the brownout state
continues for a while, thereafter the AC input again shifts to a
sufficiently high state and the plug removal occurs. In FIG. 8, t1
is the timing when the AC input falls to go into the brownout
state, t2 is the discharge timing of the peak hold capacitor, t4 is
the timing when the AC input rises and comes out of the brownout
state, and t5 is the timing when the plug removal occurred.
[0081] As seen from FIG. 8, the reset pulse of the timer circuit 54
is generated in synchronization with the output of the AND gate G6
of the timer reset control circuit 57, and as a result, the reset
pulse is synchronized with the output of the comparator 56B. In
order to measure various timer times more accurately, the reset
pulse is generated for each of the rising edge and the falling edge
of the output of the comparator 56B. The timer circuit 54 is
configured to start the time measuring operation from 0 each time
the reset pulse is input.
[0082] As seen from FIG. 8, the reset pulse of the timer circuit 54
is not generated in a period T1 from the timing t1 when the AC
input falls to go into the brownout state to the timing t3 when the
brownout detection signal changes to a high level, or in a period
T2 from the timing t5 when the plug removal occurs to the timing t6
when the X capacitor discharge signal changes to a high level.
Thus, the timer circuit 54 measures the delay time Td3 for
detecting brownout from the timing t1, measures the delay time Td2
for detecting plug removal from the timing t5, and can change the
respective corresponding signals.
[0083] The discharge signal (pulse) "DISCHARGE" of the peak hold
capacitor is output at the timing t2 when the delay time Td1 of the
discharge of the peak hold circuit 56A elapses from the timing t1
when the AC input goes into the brownout state. After the capacitor
C4 of the peak hold circuit 56A is discharged, the electric charges
corresponding to the AC input which decreased in the brownout are
charged. Thereby, the plug removal detection level changes to a
lower level, and thereafter the plug removal state is determined by
this detection level. The detection level is in the rising
direction when the AC input rises to come out of the brownout
state. Thus, since it is not necessary to discharge the capacitor
C4 of the peak hold circuit 56A, the discharge signal (pulse)
"DISCHARGE" is not generated at the timing t4. The discharge pulse
does not need to completely discharge the electric charges in the
capacitor C4, and it is sufficient that the discharge pulse has a
pulse width which can be lowered to be equal to or lower than the
brownout detection level.
[0084] FIG. 9 shows voltage waveforms of the components in the
power supply control IC 13 in a case where the AC input falls to
shift to the brownout state during the switching control operation
by the power supply control IC 13 with a sufficiently high AC
input, and the plug removal occurs during the brownout. In FIG. 9,
t11 is the timing when the AC input falls to go into the brownout
state, and t14 is the timing when the plug removal occurs.
[0085] As seen from FIG. 9, at the timing t13 which is the timing
after measuring the delay time Td3 for detecting brownout from the
timing t11 when the AC input falls to go into the brownout state,
the brownout detection signal changes to a high level, and
switching is stopped. Even in a case where the plug removal occurs
during the brownout, the discharge signal of the X capacitor
changes to a high level at the timing t15 which is the timing after
measuring the delay time Td2 from the timing t14. At the timing t12
which is the timing after the delay time Td1 elapses from the
timing t11 of going into the brownout state, the discharge signal
(pulse) of the capacitor C4 of the peak hold circuit 56A is
output.
[0086] FIG. 10 shows voltage waveforms of the components in the
power supply control IC 13 in a case where the AC input falls to
shift to the brownout state during the switching control operation
by the power supply control IC 13 with a sufficiently high AC
input, thereafter the Ac input returns to the sufficiently high
state before the delay time Td3 passes, and the plug removal
occurs. In FIG. 10, t21 is the timing when the AC input falls to go
into the brownout state, and t23 is the timing when the plug
removal occurs.
[0087] As seen from FIG. 10, since the brownout state is temporary,
the brownout detection signal does not change to a high level and
the switching continues. On the other hand, the discharge signal of
the X capacitor changes to a high level at the timing t24 which is
the timing after the delay time Td2 is measured from the timing t23
when the plug removal occurs. The discharge signal (pulse) of the
capacitor of the peak hold circuit 56A is output at the timing t22
when the delay time Td1 elapses from the timing t21 when the AC
input goes into the brownout state.
[0088] Among the timing charts of FIGS. 8 to 10, FIGS. 8 and 10
corresponds to FIG. 7A, and FIG. 9 corresponds to FIG. 7C. Though
the detailed timing chart is omitted for a case where the plug
removal occurs at the timing as shown in FIG. 7B or 7D, according
to the brownout and plug removal detection circuit 50 in the
example, in each case, the timer circuit 54 is reset to start
measuring the delay time Td2 at the timing t0 which is the last
timing when the output of the comparator 56B for detecting the plug
removal changed to a high level in FIGS. 7B and 7D. At the time
when Td2 is measured, the identification control circuit 58
determines that plug removal occurred and changes the discharge
signal of X capacitor to a high level and discharges the X
capacitor.
[0089] As mentioned above, according to the example, even if the AC
plug is removed in the brownout state, it is possible to detect the
plug removal and discharge the X capacitor. Furthermore, even if
the input level is brown-in, in a case where the AC plug is removed
at the timing of low input level, it is possible to discharge the X
capacitor without detecting the brownout by mistake.
[0090] Though the present invention has been described in detail on
the basis of the embodiment, the present invention is not limited
to the embodiment or the example. For example, in the embodiment
(FIG. 3), the discharge switch Sd is directly controlled by the
discharge signal XCD of the X capacitor output from the
identification control circuit 58 at the subsequent stage of the
timer circuit 54. However, the discharge switch Sd may be
controlled by a control signal generated with a logic of the
starting control circuit 41 by inputting the discharge signal XCD
of the X capacitor to the starting control circuit 41 as shown by
the dotted line in FIG. 3. Though the resistor Rd for discharging
and the discharge switch Sd are provided in series with the switch
S0 for power supply between the high voltage input starting
terminal HV and the ground point, the resistor Rd for discharging
and the discharge switch Sd may be provided between the high
voltage input starting terminal HV and the ground point. In such a
case, the MOS transistor forming the discharge switch Sd needs to
be a high withstand voltage MOS transistor (having a withstand
voltage which can deal with the AC input).
[0091] In the embodiment, though the common timer circuit 54
measures three delay times that are the brownout detection delay
time, the plug removal detection delay time and the discharge delay
time of the peak hold circuit, the common timer circuit 54 may
measure the two delay times that are the brownout detection delay
time and the plug removal detection delay time, and a separate
timer circuit may measure the discharge delay time of the peak hold
circuit that is relatively short.
[0092] The switching transistor SW which allows an electric current
to flow intermittently in the primary-side winding wire of the
transformer is an element separate from the power supply control IC
13. However, the switching transistor SW may be incorporated into
the power supply control IC 13 as a single semiconductor integrated
circuit.
[0093] Though the embodiment has been described for a case where
the present invention is applied to the power supply control IC
included in a flyback type AC-DC converter, the present invention
can be applied to a power supply control IC included in an AC-DC
converter of a forward type and a quasi-resonant type, and further
applied to a power supply control IC included in an AC-DC converter
of a PSR (Primary Side Regulation) type which controls the output
voltage on the secondary side by only the information obtained on
the primary side.
[0094] According to an aspect of the present invention, there is
provided a semiconductor device for switching power supply control
including: a high voltage input starting terminal to which a
voltage obtained by rectifying an alternating current voltage is
input; a discharger which is provided between the high voltage
input starting terminal and a ground point; and an input state
detection circuit which is connected to the high voltage input
starting terminal and detects an input state of the alternating
current voltage, wherein the input state detection circuit
includes: a voltage divider which includes a high withstand voltage
resistor that divides the voltage of the high voltage input
starting terminal; a peak hold circuit which includes a capacitor
and a discharge switch of the capacitor, and holds a peak voltage
of a voltage divided by the voltage divider; a first comparator
which compares the voltage divided by the voltage divider with a
voltage obtained by proportional reduction of the voltage held by
the peak hold circuit, and which detects generation of a plug
removal state; a second comparator which compares the voltage
divided by the voltage divider with a predetermined voltage, and
detects generation of a brownout state; a timer circuit which
measures a predetermined time that is set in advance; and a control
signal generation circuit which generates a signal to turn on the
discharger or a signal to stop outputting of a switching control
signal based on an output of the timer circuit, Td1, Td2 and Td3
are set to have a relationship of Td1<Td2<Td3, Td1 being a
delay time until the capacitor is discharged after an output of the
second comparator is changed in accordance with decrease of an
alternating current input, Td2 being a delay time for determining
the plug removal state, and Td3 being a delay time for determining
the brownout state, and at least the delay time Td2 and the delay
time Td3 are measured by a common timer circuit.
[0095] According to the above configuration, the delay time Td1
until the capacitor is discharged, the delay time Td2 for
determining the plug removal state and the delay time Td3 for
determining the brownout state are set in a relationship of
Td1<Td2<Td3. Thus, in a case where the brownout detection
function and the discharge function of the X capacitor are
provided, it is possible to accurately detect the brownout state
and the plug removal state by using the high voltage input starting
terminal as the detection terminal for both of the functions. Since
the timer circuit is shared, it is possible to avoid the increase
in chip size and suppress the generation of noise. Furthermore, the
voltage divider which is connected to the high voltage input
starting terminal can be used as a common means for determining the
plug removal state not only for detecting the brownout state. Thus,
it is possible to reduce the chip size compared with a case where
separate means are provided.
[0096] Preferably, the semiconductor device for switching power
supply control includes: a clock generation circuit which generates
a clock signal of a predetermined period; and a switching control
signal generation circuit which generates the switching control
signal based on the clock signal from the clock generation circuit,
wherein in response to that the delay time Td2 is measured by the
timer circuit, the control signal generation circuit generates and
outputs a control signal for turning on the discharger, and in
response to that the delay time Td3 is measured by the timer
circuit, the control signal generation circuit generates a brownout
detection signal and supplies the generated brownout detection
signal to the switching control signal generation circuit to stop
outputting of the switching control signal.
[0097] By the above configuration, it is possible to perform the
desired control accurately by determining whether the current state
is the state in which the AC plug is removed and the discharging of
X capacitor is required, or whether the current state is in the low
AC input level (brownout) state and requiring stopping of the
outputting of switching control signal (GATE) on the basis of the
voltage input to the high voltage input starting terminal. Even if
the AC plug is removed in the brownout state, it is possible to
detect the removal and discharge the X capacitor. Even if the input
level is brown-in, in a case where the AC plug is removed at the
timing of low input level, it is possible to discharge the X
capacitor without detecting the brownout by mistake.
[0098] Preferably, in the semiconductor device for switching power
supply control, the control signal generation circuit generates a
control signal for turning on the discharge switch of the peak hold
circuit to discharge the capacitor in response to that the delay
time Td1 is measured by the timer circuit.
[0099] If the change width in the AC peak voltage is large when the
AC input level changes to the brownout from the brown-in (t1 in
FIG. 8), the peak hold circuit cannot hold the AC peak value after
the change instantly. Thus, depending on conditions, the threshold
of plugout detection may exceed the AC peak value after the change,
leading to the wrong detection determining that the plug was
removed though the AC input merely becomes lower than the
predetermined value and the AC input is in the plug-in state. By
the above configuration, the electric charges held in the peak hold
circuit (capacitor) can be discharged at the time when the timer
circuit measures the delay time Td1. Thus, since the threshold of
plugout detection is set at an appropriate level (equal to or lower
than the AC peak value after change), it is possible to prevent the
wrong detection.
[0100] Preferably, in the semiconductor device for switching power
supply control, the common timer circuit is reset and starts a time
measuring operation in response to output change of the first
comparator and the second comparator, and resetting of the timer
circuit is prohibited even when an output of the first comparator
changes, until the second comparator detects start of the brownout
state and the delay time Td3 elapses.
[0101] By the above configuration, it is possible to appropriately
and easily generate a reset signal of the timer circuit. In
addition, it is possible to measure the delay time Td2 for
determining the plug removal state and the delay time Td3 for
determining the brownout state by a common timer circuit since the
timer circuit is not reset during detection of the brownout
state.
[0102] Preferably, in the semiconductor device for switching power
supply control, the common timer circuit measures the delay time
Td1, the delay time Td2, and the delay time Td3.
[0103] By the above configuration, the three delay times can be
measured by using a common timer circuit. Thus, it is possible to
avoid the increase in chip size by reducing the possession area of
the timer circuit, and suppress the generation of noise since there
is no simultaneous operation of a plurality of timer circuits
having different oscillation frequencies.
[0104] In a case where the timer circuit is formed of a frequency
division circuit having a plurality of flip-flops in a cascade
connection and the delay times Td1, Td2 and Td3 are set to satisfy
Td2=2Td1 and Td3=4Td1, for example, the time measuring signal of
Td2 is obtained by taking out from a half step of the time
measuring signal of Td3, and the time measuring signal of Td1 is
obtained by taking out from a quarter step of the time measuring
signal of Td3. Thus, it is possible to easily generate each time
measuring signal (timeout signal).
[0105] Preferably, the semiconductor device for switching power
supply control includes: a switch which is connected between the
high voltage input starting terminal and a power supply terminal to
which a voltage obtained by rectifying an induced voltage in an
auxiliary winding wire of a transformer is applied; and a starting
control circuit which controls the switch when a voltage is applied
to the high voltage input starting terminal, wherein the switch
includes a depression type N-channel MOS transistor with a high
withstand voltage, and the discharger is connected in series with
the switch between the high voltage input starting terminal and the
ground point.
[0106] By the above configuration, it is not necessary to form the
discharger with a high withstand voltage element, the discharger
discharging the electric charges of the high voltage input starting
terminal when the plug removal state occurs.
[0107] According to an aspect of the present invention, in the
semiconductor device for control that includes the brownout
detection function and the X capacitor discharge function, it is
possible to accurately detect the brownout state and the plug
removal state by using the high voltage input starting terminal as
a detection terminal for detecting both of the states. Since a
timer circuit necessary for the brownout detection function and the
X capacitor discharge function is shared for both of the functions,
there is an advantage that it is possible to reduce the possession
area of the timer circuit to avoid the increase in chip size, and
suppress the generation of noise.
[0108] Although some embodiments of the present invention have been
described and illustrated in detail, the disclosed embodiments are
made for purposes of not limitation but illustration and example
only. The scope of the present invention should be interpreted by
terms of the appended claims.
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